1. Field of the Invention
The present invention relates to a display system capable of selectively displaying graphic display data and character display data and a combination of the two types of data on two display units.
2. Description of the Prior Art
In recent years, display systems have become increasingly advanced. Even personal computers are now being provided with display systems capable of the display of not only character information, such as letters and numerals, but also graphic information, such as figures, curves, circle graphs, and histograms.
The display of an actual graph requires the combination of graphic and character information. In the prior art, this has been achieved by storing the combined graphic display data and character display data in an image memory having a capacity sufficient for a display picture and by displaying the data on a single cathode ray tube (CRT). The prior art, however, has suffered from the problem of inadvertent deletion of characters due to interference from the graphic display when adjusting the display, for example, changing colors, enlarging figures, and changing positions, and the problem of an overly crowded display picture when there are too many characters and symbols for graph notations.